The present invention relates to metal-cutting inserts having cutting edges formed of a superhard abrasive, such as polycrystalline cubic boron nitride (i.e., PCBN) or polycrystalline diamond (i.e., PCD), for example, and methods of making same.
Metal cutting inserts having cutting edges formed of a superhard abrasive, such as PCD, are usually used for the machining of non-ferrous alloys such as brass, magnesium and aluminum, and the like, whereas inserts with cutting edges formed of a superhard abrasive, such as PCBN, are usually used for the machining of cast iron and hardened steel and the like. The inserts are made in two different ways, namely (i) by sintering, under elevated pressure and temperature, a PCBN or PCD material into a solid body that is finished to form the final insert shape, or (ii) by bonding a layer of PCBN or PCD, under elevated pressure and temperature, to a substrate (usually a cemented carbide disc), from which smaller pieces (chips) are cut out. These chips are then brazed onto a regular carbide insert and ground to the finished size. Inserts are relatively expensive to produce in that way due to the many steps the product must undergo before it is finished. Also, usually only one or two superhard corners per insert are available.
Disclosed in Dodsworth U.S. Pat. No. 4,866,885 is a technique for making metal-cutting inserts wherein shallow recesses are formed in a surface of a cemented carbide substrate at locations spaced inwardly from an outer periphery of the substrate. Each recess is filled with hard abrasive particles such as PCD or PCBN. The substrate and abrasive particles are then subjected to a sintering operation at elevated temperature and pressure conditions, whereupon the abrasive particles become sintered to each other and bonded to the carbide body. The substrate is then severed along lines extending through the abrasive bodies parallel thereto to produce a multi-cornered cutting insert having a cemented carbide substrate and abrasive cutting bodies located on one side thereof. Among the shortcomings of such a procedure are that the insert has abrasive bodies on only one side. In order to provide such bodies on the other side, additional recesses would have to be formed in that other side and filled with superhard abrasive material. Also, the wire cutting involves an added step.
It would, therefore, be desirable to increase the number of abrasive bodies on an insert in order to decrease the cost per cutting corner, and to do so without unduly increasing the number of processing steps and overall manufacturing costs.